1. Technical Field of the Invention
The present invention relates to a cosmetic or dermatological composition comprising at least one photoprotective system capable of screening out UV rays, containing at least one insoluble mineral or organic UV-screening agent, with a particle size ranging from 5 nm to 5 μm, characterized in that it also comprises at least one amphiphilic polymer comprising at least one ethylenically unsaturated monomer containing a sulfonic group, in free form or partially or totally neutralized form, and comprising at least one hydrophobic portion.
2. Description of Background/Related/Prior Art
The invention also relates to the use of these compositions for protecting the skin and the hair against the effects of ultraviolet radiation.
It is known that light radiation with wavelengths of between 280 nm and 400 nm permit tanning of the human epidermis, and that light rays with wavelengths more particularly between 280 and 320 nm, which are known as UV-B rays, cause skin burns and erythema that may harm the development of a natural tan. For these reasons, and also for aesthetic reasons, there is a constant demand for means for controlling this natural tanning in order thus to control the color of the skin; this UV-B radiation should thus be screened out.
It is also known that UV-A rays, with wavelengths of between 320 and 400 nm, which cause tanning of the skin, are liable to induce an impairment thereof, especially in the case of sensitive skin or of skin that is continually exposed to sunlight. In particular, UV-A rays cause a loss of elasticity of the skin and the appearance of wrinkles, leading to premature aging of the skin. They promote the triggering of the erythemal reaction or amplify this reaction in certain individuals and may even be the cause of phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons, for instance preserving the natural elasticity of the skin, more and more individuals wish to control the effect of UV-A rays on their skin. It is thus desirable also to screen out UV-A radiation.
Many cosmetic compositions intended for photoprotection (against UV-A and/or UV-B) of the skin have been proposed to date.
These antisun compositions are quite often in the form of an emulsion, of oil-in-water type (i.e., a cosmetically and/or dermatologically acceptable support consisting of an aqueous dispersing continuous phase and a fatty dispersed discontinuous phase) or water-in-oil type (aqueous phase dispersed in a continuous fatty phase), which contains, in varying concentrations, one or more standard lipophilic organic screening agents and/or mineral metal oxide nanopigments, capable of selectively absorbing the harmful UV radiation, these screening agents (and the amounts thereof) being selected as a function of the desired sun protection factor, the sun protection factor (SPF) mathematically expressing the ratio of the dose of UV radiation required to reach the erythema-forming threshold with the UV-screening agent to the dose of UV radiation required to reach the erythema-forming threshold without a UV-screening agent. In such emulsions, the hydrophilic screening agents are present in the aqueous phase and the lipophilic screening agents are present in the fatty phase.
Users generally prefer oil-in-water emulsions to water-in-oil emulsions, especially on account of their pleasant feel (close to water) and their presentation in the form of a milk or a non-greasy cream; however, they also more readily lose their anti-UV efficacy once they come into contact with water; the reason for this is that hydrophilic screening agents have a tendency to be lost in water, on bathing in the sea or in a swimming pool, under the shower or when practicing water sports; thus, the antisun compositions they contain, alone or combined with lipophilic screening agents, no longer provide the desired initial protection once the substrate (skin or hair) onto which they have been applied comes into contact with water.
It is possible to obtain antisun compositions with improved water resistance by using water-in-oil emulsions. The reason for this is that a hydrophilic screening agent is more water-resistant in a water-in-oil emulsion than in an oil-in-water emulsion. However, as has been mentioned above, such compositions are still not entirely satisfactory since, after they have been applied, they leave a greasy impression that users find particularly unpleasant.
Thus, there is still a need to be able to obtain antisun compositions that give the skin and/or the hair effective antisun protection, which is stable over time and water-resistant, and the cosmetic performance qualities of which are comparable to those obtained with standard oil/water emulsions.
The UV-screening agents most commonly used are organic and soluble in oils or in aqueous media; they generally contain in their structure a chromophoric group linked to a solubilizing group that is generally a fatty chain in the case of liposoluble UV-screening agents or a carboxylic or sulfonic acid group in the case of water-soluble UV-screening agents.
Micronized insoluble organic UV-screening agents with a mean particle size ranging from 10 nm to 2 μm, which have the advantage of being more effective than their soluble homologues comprising the same chromophoric group to an equivalent proportion, are known in the prior art. UV-screening agents of this type are especially described in EP-746,305 and EP-8-405,395.
Pigments or nanopigments (mean size of the primary particles: generally between 5 nm and 100 nm and preferably between 10 mu and 50 nm) of coated or uncoated metal oxides, for instance titanium oxide (amorphous or crystallized in rutile and/or anatase form), iron oxide, zinc oxide, zirconium oxide or cerium oxide nanopigments, are very frequently used in antisun formulations in combination with soluble organic UV-screening agents. Insoluble UV-screening agents of this type make it possible to increase the level of protection of the soluble organic UV-screening agents and to achieve high protection factors.
Unfortunately, it is often difficult to incorporate insoluble UV-screening agents into standard antisun formulations such as oil/water or water/oil emulsions.